The present invention relates to a fire detector having an oscillating circuit, a sampling pulse generating circuit for generating a sampling pulse on the basis of an oscillating output pulse of the oscillating circuit, a sensing circuit for producing a fire sensing signal at least at the time that the sampling pulse is transmitted, a judging circuit for producing a judging signal when the signal from the sensing circuit exceeds a predetermined level, and a fire alarm trigger signal transmitting circuit for generating a fire alarm trigger signal on the basis of the judging signal from the judging circuit and for transmitting the fire alarm trigger signal through a signal line to a fire alarm controller.
In order to monitor or check the operation of a fire detector, i.e., to check as to whether or not the fire detector is operating normally, the operational condition of the oscillator and the sensor have hitherto been checked individually. This leads to the drawback of low work efficiency with respect to the monitoring operation. In the case of a fire detector with a fire alarm trigger signal transmitting circuit of the so-called storage type which transmits an alarm trigger signal after the sensor has sensed smoke or heat or fire for more than a predetermined time period, for example, 20 seconds, the monitoring of the sensor cannot be completed until the lapse of the predetermined period after the smoke or heat has been sensed.